JP6918595B2 - Fixed anode type X-ray tube - Google Patents

Description

Embodiments of the present invention relate to fixed anode X-ray tubes.

X-ray tubes are used, for example, in medical or dental X-ray tube devices for X-ray diagnosis. This type of X-ray tube comprises a cathode, an anode target facing the cathode, and a vacuum enclosure containing the cathode and the anode target. The X-ray tube voltage applied between the anode target and the cathode accelerates thermions emitted from the filament of the cathode and enters the anode target. As a result, X-rays due to bremsstrahlung are emitted from the anode target.

Since X-rays are emitted, electric power, which is the product of the X-ray tube voltage and the X-ray tube current, is input to the anode target. By the way, about 1% or less of the power consumption is converted into X-rays, and the remaining 99% or more is converted into thermal energy. With repeated use of the X-ray tube, the anode target is repeatedly heated and cooled. The anode target has a target body and a target layer bonded to the target body.

Then, due to the difference between the coefficient of thermal expansion of the target body and the coefficient of thermal expansion of the target layer, strain may occur at the joint surface between the two. When the strain becomes large, the target layer is peeled off from the target body. At the location where the target layer is separated from the target body, the heat transfer efficiency from the target layer to the target body deteriorates, and the temperature difference between the two becomes even larger. If the X-ray tube is used as it is, the region where the focal point is formed melts or cracks occur in the target layer. From the above, the product life of the above-mentioned X-ray tube tends to be shortened.

Jikkensho 41-17859

The present embodiment provides a fixed anode type X-ray tube capable of prolonging the product life.

The fixed anode type X-ray tube according to one embodiment is
A target body having a groove including a bottom surface and an inner peripheral surface,
A front surface having a coefficient of thermal expansion different from the coefficient of thermal expansion of the target body, provided in the groove, joined to the target body to form a focal point for emitting X-rays, and a back surface joined to the bottom surface. A target layer having a side surface joined to the inner peripheral surface, and
Equipped with an anode target,
The joint surface between the target body and the target layer has a curved surface.

FIG. 1 is a schematic configuration diagram showing a fixed anode type X-ray tube according to an embodiment. FIG. 2 is an enlarged cross-sectional view showing an anode target according to the first embodiment of the above embodiment. FIG. 3 is a plan view of the anode target of the first embodiment as viewed from above the target layer. FIG. 4 is a cross-sectional view showing the anode target along line IV-IV of FIG. FIG. 5 is an exploded view of the anode target shown in FIG. FIG. 6 is an enlarged cross-sectional view showing the anode target according to the second embodiment of the above embodiment. FIG. 7 is an enlarged cross-sectional view showing the anode target of FIG. FIG. 8 is an enlarged cross-sectional view showing an anode target of a fixed anode type X-ray tube of a comparative example. FIG. 9 is a bar graph showing the ratio of stress acting on each anode target of Example 1, Example 2, and Comparative Example. FIG. 10 is an enlarged cross-sectional view showing the anode target according to the third embodiment of the above embodiment.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. It should be noted that the disclosure is merely an example, and those skilled in the art can easily conceive of appropriate changes while maintaining the gist of the invention are naturally included in the scope of the present invention. Further, in order to clarify the explanation, the drawings may schematically represent the width, thickness, shape, etc. of each part as compared with the actual embodiment, but this is just an example, and the interpretation of the present invention is used. It is not limited. Further, in the present specification and each figure, the same elements as those described above with respect to the above-mentioned figures may be designated by the same reference numerals, and detailed description thereof may be omitted as appropriate.

FIG. 1 is a schematic configuration diagram showing a fixed anode type X-ray tube according to an embodiment.

As shown in FIG. 1, the fixed anode type X-ray tube 1 includes a cathode 2, an anode target 3, a vacuum enclosure 4, and a plurality of pin assemblies such as a pin assembly 15. The cathode 2 has a filament (electron emission source) 2f that emits electrons (thermions) and a focusing electrode 2e. Each pin assembly is airtightly attached to the vacuum enclosure 4 and is located both inside and outside the vacuum enclosure 4. For example, the pin assembly 15 is used to apply a negative high voltage and filament current to the filament 2f. Although not shown, a pin assembly for the focusing electrode 2e is used to apply a negative high voltage to the focusing electrode 2e.

The anode target 3 includes a target main body 31, a target layer 32, and an anode extending portion 33. The target main body 31 has a flat front surface 31f located on the side facing the filament 2f, and a groove 34 formed in the front surface 31f. The target layer 32 is provided in the groove 34 and is joined to the target main body 31. When forming the target layer 32, it can be formed by using various conventionally known methods. For example, the target layer 32 can be formed directly in the groove 34 by thermal spraying. In another example, the preformed target layer 32 may be brazed to the groove 34. The target layer 32 emits X-rays when the electrons emitted from the filament 2f and focused by the focusing electrode 2e are impacted. In other words, the target layer 32 is formed with a focal point F that emits X-rays due to the impact of electrons.

The target layer 32 has a coefficient of thermal expansion different from that of the target body 31. The target body 31 is made of a metal such as copper (Cu) or an alloy thereof as a highly thermally conductive metal. The target layer 32 is formed of a metal such as tungsten (W) or an alloy thereof as a metal having a melting point higher than that of the material used for the target body 31. In this embodiment, the target body 31 is made of copper and the target layer 32 is made of tungsten.

The anode extending portion 33 is formed in a columnar shape and is physically connected to the target main body 31 to fix the target main body 31. The anode extension 33 is airtightly attached to the vacuum enclosure 4 and is located both inside and outside the vacuum enclosure 4. The heat generated in the target layer 32 due to the impact of electrons on the target layer 32 is released to the outside of the X-ray tube 1 via the target body 31 and the anode extending portion 33.

The vacuum enclosure 4 houses the cathode 2, the target body 31, the target layer 32, and the like. The internal space of the vacuum enclosure 4 is decompressed and is in a vacuum state. At least a part of the vacuum enclosure 4 is made of a material that transmits X-rays emitted from the target layer 32. For example, the vacuum enclosure 4 has a glass container formed by using borosilicon glass and having X-ray transparency, and a metal container formed by using Kovar.

The voltage and current output from the power supply unit on the outside of the X-ray tube 1 are given to the two pin assemblies including the single pin assembly 15, and thus to the filament 2f. As a result, the filament 2f emits an electron. The power supply unit also applies a predetermined voltage to the cathode 2 and the anode target 3. In this embodiment, a negative high voltage is applied to the cathode 2 and a positive high voltage is applied to the anode target 3. Since the X-ray tube voltage is applied between the anode target 3 and the cathode 2, the electrons emitted from the filament are accelerated and incident on the target layer 32 as an electron beam. That is, an X-ray tube current flows from the cathode 2 to the target layer 32. The focusing electrode 2e, which serves as a cathode potential, can focus an electron beam (electrons) from the filament 2f toward the anode target 3.

The target layer 32 emits X-rays when an electron beam is incident on the target layer 32, and the X-rays pass through the vacuum enclosure 4 and are emitted to the outside of the X-ray tube 1.

Next, (1) the anode target 3 according to the first embodiment, (2) the anode target 3 according to the second embodiment, (3) the anode target 3 according to the comparative example, and (4) the stress acting on various anode targets 3. The ratio and (5) the anode target 3 according to the third embodiment will be described.

(Example 1)
First, the anode target 3 according to the first embodiment will be described. FIG. 2 is an enlarged cross-sectional view showing a part of the anode target 3 according to the first embodiment. FIG. 3 is a plan view of the anode target 3 of the first embodiment as viewed from above of the target layer 32.

As shown in FIGS. 2 and 3, the groove 34 formed in the target main body 31 has a bottom surface 34b and an inner peripheral surface 34i. In the first embodiment, the bottom surface 34b has a perfect circular shape and is a plane parallel to the front surface 31f. The opening 34o of the groove 34 is located on the same plane as the front surface 31f and has a perfect circular shape. The inner diameter of the opening 34o is larger than the diameter of the bottom surface 34b. The inner peripheral surface 34i extends over the entire area from the opening 34o to the bottom surface 34b and is not parallel to the depth direction d of the groove 34. The depth direction d is perpendicular to the front surface 31f. The inner peripheral surface 34i has a curved surface in at least a part of the entire area from the opening 34o to the bottom surface 34b.

The target layer 32 has a disk shape. The target layer 32 has a front surface 32f on which the focal point F is formed, a back surface 32b, and a side surface 32s. The back surface 32b is joined to the bottom surface 34b of the groove 34, and the side surface 32s is joined to the inner peripheral surface 34i of the groove 34. The side surface 32s is not parallel to the thickness direction (depth direction d) of the target layer 32 over the entire area from the front surface 32f to the back surface 32b. The side surface 32s has a curved surface in at least a part of the entire area from the front surface 32f to the back surface 32b.

The joint surface between the target body 31 and the target layer 32 has a curved surface at least in part.

FIG. 4 is a cross-sectional view showing the anode target 3 along the line IV-IV of FIG. Note that FIG. 4 shows a cross section passing through the groove 34 and the target layer 32 in the depth direction d.

As shown in FIG. 4, the inner peripheral surface 34i has a first surface S34i having a curved surface shape at least on the bottom surface 34b side. The first surface S34i is provided over the entire circumference of the inner peripheral surface 34i and extends continuously from the bottom surface 34b. In the first embodiment, since the entire first surface S34i has a curved surface shape from the opening 34o toward the bottom surface 34b, the entire inner peripheral surface 34i is the first surface S34i.

The side surface 32s has a second surface S32s at least in part. The second surface S32s faces the first surface S34i and has a curved surface shape along the first surface S34i. The second surface S32s is provided over the entire circumference of the side surface 32s and extends continuously from the back surface 32b. In the first embodiment, since the entire second surface S32s has a curved surface shape from the front surface 32f to the back surface 32b, the entire side surface 32s is the second surface S32s.

The joint surface between the first surface S34i and the second surface S32s has a curved surface.

FIG. 5 is an exploded view of the anode target 3 shown in FIG. In addition, also in FIG. 5, the cross section passing through the groove 34 and the target layer 32 in the depth direction d is shown.

As shown in FIG. 5, of the inner peripheral surface 34i of the groove 34, a virtual straight line connecting the end E1 on the opening 34o side and the end E2 on the bottom surface 34b side is defined as the first straight line L1. Of the side surface 32s, a virtual straight line connecting the end E3 on the front surface 32f side and the end E4 on the back surface 32b side is referred to as a second straight line L2. Then, the first surface S34i is located on the opposite side of the central CE of the groove opening 34o with respect to the first straight line L1. The second surface S32s is located on the opposite side of the surface 32f with respect to the second straight line L2.

(Example 2)
Next, the anode target 3 according to the second embodiment will be described. FIG. 6 is an enlarged cross-sectional view showing the anode target 3 according to the second embodiment.

As shown in FIG. 6, in the second embodiment, the shapes of the groove 34 and the target layer 32 are different from those in the first embodiment. The inner peripheral surface 34i does not have a curved surface shape from the opening 34o toward the bottom surface 34b, and extends linearly along the first straight line L1. The side surface 32s does not have a curved surface shape from the front surface 32f to the back surface 32b, and extends linearly along the second straight line L2. Needless to say, the inner peripheral surface 34i and the side surface 32s are not parallel to the depth direction d, respectively.

Here, the joint surface between the bottom surface 34b and the back surface 32b is referred to as the first joint surface S1. The joint surface between the inner peripheral surface 34i and the side surface 32s is designated as the second joint surface S2. The angle θ between the first joint surface S1 and the second joint surface S2 is an obtuse angle (90 ° <θ <180 °). In Example 2, θ = 140 °.

FIG. 7 is an enlarged cross-sectional view showing the anode target 3 of FIG.

As shown in FIG. 7, in the second embodiment, the groove 34 and the target layer 32 each have the shape of a true truncated cone. The inner diameter D1 of the groove 34 is smaller on the bottom surface 34b side than on the opening 34o side of the groove 34. In other words, the area of the bottom surface 34b is smaller than the area of the opening 34o. The outer diameter D2 of the target layer 32 is smaller on the back surface 32b side than on the front surface 32f side. In other words, the area of the back surface 32b is smaller than the area of the front surface 32f.

The shapes of the groove 34 and the target layer 32 are not limited to the truncated cones, and can be deformed in various ways. For example, the shape of the groove 34 and the target layer 32 may be another frustum such as an elliptical frustum, or a polygonal frustum such as a quadrangular frustum.

(Comparison example)
Next, the anode target 3 according to the comparative example will be described. FIG. 8 is an enlarged cross-sectional view showing the anode target 3 according to the comparative example.

As shown in FIG. 8, in the comparative example, the shapes of the groove 34 and the target layer 32 are different from those of the first and second embodiments. The shape of each of the groove 34 and the target layer 32 is columnar. The inner peripheral surface 34i and the side surface 32s extend parallel to each other in the depth direction d.

(Stress ratio)
Next, the ratio of the stress (thermal stress) acting on the anode target 3 of each of the first, second, and comparative examples will be described. FIG. 9 is a bar graph showing the ratio of stress acting on each of the anode targets 3 of Examples 1, 2, and Comparative Example.

As shown in FIG. 9, the graph g1 shows the stress acting on the boundary B between the inner peripheral surface 34i and the side surface 32s in the vicinity of the bottom surface 34b and the back surface 32b in the anode target 3 of the comparative example. Graph g2 shows the stress acting on the boundary B in the anode target 3 of Example 2. Graph g3 shows the stress acting on the boundary B in the anode target 3 of Example 1.

When deriving the graphs g1, g2, and g3, the simulation was performed under the same conditions, such as making the amount of heat input to each target layer 32 the same. Further, the stress ratios of the graphs g1, g2 and g3 are standardized, and the stress ratio of the comparative example is set to 1. The stress ratio of Example 2 was substantially 0.7, and the stress ratio of Example 1 was substantially 0.4.

As can be seen from FIG. 9, by making the shapes of the groove 34 and the target layer 32 into a truncated cone, the stress applied to the boundary B is relaxed to substantially 70% of the comparative example. Further, by providing the joint surface between the target body 31 and the target layer 32 with a curved surface, the stress applied to the boundary B is relaxed to substantially 40% of the comparative example.

(Example 3)
Next, the anode target 3 according to the third embodiment will be described. FIG. 10 is an enlarged cross-sectional view showing the anode target 3 according to the third embodiment.

As shown in FIG. 10, the groove 34 and the target layer 32 each have the shape of a truncated cone. However, in the third embodiment, the inner diameter D1 of the groove 34 is larger on the bottom surface 34b side than on the opening 34o side. Further, the outer diameter D2 of the target layer 32 is larger on the back surface 32b side than on the front surface 32f side. The target layer 32 of Example 3 can be formed directly in the groove 34 by, for example, thermal spraying.

According to the X-ray tube 1 according to the above-described embodiment configured as described above, the X-ray tube 1 includes an anode target 3 including a target main body 31 and a target layer 32. In the first embodiment, the joint surface between the target body 31 and the target layer 32 has a curved surface. In the second embodiment, the angle θ is an obtuse angle at the joint surface between the target body 31 and the target layer 32. Since the stress applied to the boundary B can be relaxed, the deformation of the target layer 32 can be suppressed even if the target layer 32 receives heat input. Further, since it is possible to suppress the occurrence of strain on the joint surface between the target body 31 and the target layer 32, it is possible to make it difficult for the target layer 32 to be peeled off from the target body 31.

In the third embodiment, the inner peripheral surface 34i of the target main body 31 presses the side surface 32s of the target layer 32. From the above, even if the target layer 32 of the third embodiment receives heat input, the deformation of the target layer 32 can be suppressed, and the target layer 32 can be made difficult to peel off from the target main body 31.

In any of the target layers 32 of Examples 1 to 3, it is possible to suppress a decrease in the heat transfer path from the target layer 32 to the target main body 31, so that the heat generated in the target layer 32 can be satisfactorily transferred to the target main body 31. Can be communicated. Then, the X-ray tube 1 can suppress deformation of the target layer 32 without using a third member such as an anode hood that presses the target layer 32.

From the above, it is possible to obtain a fixed anode type X-ray tube 1 capable of prolonging the product life.

Although embodiments of the present invention have been described, the above embodiments are presented as examples and are not intended to limit the scope of the invention. The novel embodiment can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. The above-described embodiment and its modifications are included in the scope and gist of the invention, and are also included in the scope of the invention described in the claims and the equivalent scope thereof .
The inventions described in the claims of the original application of the present application are described below.
[1]
A target body having a groove including a bottom surface and an inner peripheral surface,
A front surface having a coefficient of thermal expansion different from the coefficient of thermal expansion of the target body, provided in the groove, joined to the target body to form a focal point for emitting X-rays, and a back surface joined to the bottom surface. A target layer having a side surface joined to the inner peripheral surface, and
Equipped with an anode target,
The joint surface between the target body and the target layer has a curved surface.
Fixed anode type X-ray tube.
[2]
The inner peripheral surface has a first surface having a curved surface shape at least on the bottom surface side.
The side surface has a second surface facing the first surface and having a curved surface shape along the first surface.
The joint surface between the first surface and the second surface has a curved surface.
The fixed anode type X-ray tube according to [1].
[3]
The first surface is provided over the entire circumference of the inner peripheral surface.
The second surface is provided over the entire circumference of the side surface.
The fixed anode type X-ray tube according to [2].
[4]
In a cross section passing through the groove and the target layer in the depth direction of the groove, the first surface is located on the opposite side of the opening of the groove with respect to the first straight line, and the second surface is relative to the second straight line. Located on the opposite side of the surface
The first straight line is a straight line connecting the end on the opening side and the end on the bottom surface side of the inner peripheral surface.
The second straight line is a straight line connecting the end on the front surface side and the end on the back surface side of the side surface.
The fixed anode type X-ray tube according to [2].
[5]
A target body having a groove including a bottom surface and an inner peripheral surface,
A front surface having a coefficient of thermal expansion different from the coefficient of thermal expansion of the target body, provided in the groove, joined to the target body to form a focal point for emitting X-rays, and a back surface joined to the bottom surface. A target layer having a side surface joined to the inner peripheral surface, and
Equipped with an anode target,
The angle between the first joint surface between the bottom surface and the back surface and the second joint surface between the inner peripheral surface and the side surface is an obtuse angle.
Fixed anode type X-ray tube.
[6]
The groove and the target layer each have the shape of a truncated cone.
The inner diameter of the groove is smaller on the bottom surface side than on the opening side of the groove.
The outer diameter of the target layer is smaller on the back surface side than on the front surface side.
The fixed anode type X-ray tube according to [5].

1 ... X-ray tube, 2 ... Cathode, 3 ... Anode target, 4 ... Vacuum enclosure,
31 ... target body, 34 ... groove, 34b ... bottom surface, 34i ... inner peripheral surface, 34o ... opening,
S34i ... 1st surface, 32 ... Target layer, 32f ... Front surface, 32b ... Back surface,
32s ... side surface, S32s ... second surface, F ... focus, S1 ... first joint surface, S2 ... second joint surface,
E1, E2, E3, E4 ... end, L1 ... first straight line, L2 ... second straight line, θ ... angle, d ... direction.

Claims (4)

A target body having a groove including a bottom surface and an inner peripheral surface,
A front surface having a coefficient of thermal expansion different from the coefficient of thermal expansion of the target body, provided in the groove, joined to the target body to form a focal point for emitting X-rays, and a back surface joined to the bottom surface. A target layer having a side surface joined to the inner peripheral surface, and
Equipped with an anode target,
The joint surface between the target body and the target layer has a curved surface.
Fixed anode type X-ray tube. The inner peripheral surface has a first surface having a curved surface shape at least on the bottom surface side.
The side surface has a second surface facing the first surface and having a curved surface shape along the first surface.
The joint surface between the first surface and the second surface has a curved surface.
The fixed anode type X-ray tube according to claim 1. The first surface is provided over the entire circumference of the inner peripheral surface.
The second surface is provided over the entire circumference of the side surface.
The fixed anode type X-ray tube according to claim 2. In a cross section passing through the groove and the target layer in the depth direction of the groove, the first surface is located on the opposite side of the opening of the groove with respect to the first straight line, and the second surface is relative to the second straight line. Located on the opposite side of the surface
The first straight line is a straight line connecting the end on the opening side and the end on the bottom surface side of the inner peripheral surface.
The second straight line is a straight line connecting the end on the front surface side and the end on the back surface side of the side surface.
The fixed anode type X-ray tube according to claim 2.

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